Search PubMed⌕ Search

Biomedical subjects

H Yu

Publications and source records attributed to H Yu.

At least 559 records · Page 31Linked to original sources
PubMed1995

Structure of guanine-nucleotide-exchange factor human Mss4 and identification of its Rab-interacting surface.

Guanine-nucleotide-exchange factors (GEFs) promote the exchange of GDP for GTP in Ras GTPases, and thereby positively regulate their functions. Members of the Sec4/Ypt1/Rab branch of the Ras superfamily are essential for vesicular transport. A GEF for a subset of Rab proteins, termed mammalian suppressor of Sec4 (Mss4), has been identified. Here we use multidimensional NMR to determine the structure of human Mss4 (hMss4), which is the first tertiary structure established for a protein with GEF activity. Mss4 contains a central beta-sheet sandwiched between two small sheets. It also binds a Zn2+ ion through Cys 23, Cys 26, Cys 94 and Cys 97. The Rab-binding surface of hMss4 has subsequently been delineated using chemical-shift perturbation experiments and site-directed mutagenesis. The active site of hMss4 involves the Zn(2+)-binding region and a neighbouring loop.

Amino Acid Sequence↗
PubMed1995

Molecular cloning of the human ryudocan promoter.

The promoter region of human ryudocan was isolated from a human lambda dash genomic library and cloned into pBluescript. The 5'flanking region contained a classical TATA box and GC rich regions that are commonly found in constitutively expressed genes. Two fusion gene constructs, one of 898 bp and the other of 480 bp of the 5' flanking DNA coupled to the luciferase gene, were transiently expressed in a mouse endothelioma cell line and in human umbilical endothelial cell cultures. Both constructs were capable of driving luciferase expression; the 898 bp construct produced greater levels of luciferase activity than the 480 bp construct in both cell types examined. Analysis of the sequence revealed the presence of several potential sites for nuclear transcription factor binding; the relevance of these sites is presently unknown.

Base Sequence↗
PubMed1995

Cloning, Zn2+ binding, and structural characterization of the guanine nucleotide exchange factor human Mss4.

The Sec4/Ypt1/Rab family of small GTP-binding proteins are involved in the regulation of intracellular vesicular transport. A rat gene, mss4, that encodes a guanine nucleotide exchange factor (GEF) for Sec4 was recently cloned by its ability to rescue defects in protein transport of a yeast temperature-sensitive (ts) mutant, sec4-8. We describe herein the cloning, bacterial expression, and biochemical characterization of human Mss4. As expected, both the cDNA and its encoded amino acid sequences are highly conserved between the human and rat mss4. Soluble and functional Mss4 protein was obtained by expressing the gene as a glutathione-S-transferase fusion protein in Escherichia coli. Subsequent biochemical analysis revealed that Mss4 binds 1 equiv of Zn2+, and zinc is essential for the stability of the protein. Utilizing multidimensional heteronuclear NMR techniques, we assigned most of the 1H, 15N, and 13C resonances of this 14-kDa protein. Its secondary structure was also deduced from slowly exchanging amide protons, characteristic NOEs, and 3JNH-C alpha H coupling constants. The protein contains a central seven-stranded antiparallel beta sheet, flanked by two small beta sheets. Many resonances pertaining to a loop region of the molecule cannot be identified, suggesting that it might be involved in local movements. These studies provide the first structural insights into a protein possessing GEF activity.

Amino Acid Sequence↗
PubMed1995

Dissociation of mitogen-activated protein kinase activation from the oxidative burst in differentiated HL-60 cells and human neutrophils.

In human polymorphonuclear leukocytes (PMNs), mitogen-activated protein kinases (MAPKs), also known as extracellular signal-regulated kinases (Erks), are activated within minutes upon stimulation with either chemoattractant formyl-Met-Leu-Phe (fMLP) or phorbol 12-myristate 13-acetate (PMA). This activation of MAPKs coincides with the formation of superoxide anion, which occurs through the activation of a multiple-component NADPH oxidase pathway. MAPKs have thus been suggested to be involved in signal transduction leading to the oxidative burst. To investigate whether MAPK activation plays a central role in the oxidative burst, we evaluated the effect of cAMP on MAPK activation induced by fMLP and PMA. cAMP inhibits many PMN functional responses, including the oxidative burst, and has recently been shown to reduce growth factor- and PMA-induced MAPK activities in a variety of cells. We found that in differentiated, neutrophil-like HL-60 cells, while cAMP reduced PMA-induced MAPK activation, it had no effect on fMLP-induced MAPK activation. Despite the presence of unchanged levels of activated MAPKs, the fMLP-induced oxidative burst was substantially diminished by cAMP. By contrast, O2-production induced by PMA remained the same even though MAPK activation was inhibited. In PMNs, although the levels of O2-induced by either 10 ng/ml or 100 ng/ml PMA were similar, only 100 ng/ml could stimulate MAPK activation, suggesting that the oxidative burst could occur in the absence of detectable activation of MAPKs. As in HL-60 cells, cAMP inhibited the O2-production in fMLP-stimulated PMNs but had no effect on MAPK activity. These results demonstrate that, while MAPK activation coincides with PMN activation, it can be dissociated from the oxidative burst.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1995

Purification and properties of wild-type and exonuclease-deficient DNA polymerase II from Escherichia coli.

Wild-type DNA polymerase II (pol II) and an exonuclease-deficient pol II mutant (D155A/E157A) have been overexpressed and purified in high yield from Escherichia coli. Wild-type pol II exhibits a high proofreading 3'-exonuclease to polymerase ratio, similar in magnitude to that observed for bacteriophage T4 DNA polymerase. While copying a 250-nucleotide region of the lacZ alpha gene, the fidelity of wild-type pol II is high, with error rates for single-base substitution and frameshift errors being < or = 10(-6). In contrast, the pol II exonuclease-deficient mutant generated a variety of base substitution and single base frameshift errors, as well as deletions between both perfect and imperfect directly repeated sequences separated by a few to hundreds of nucleotides. Error rates for the pol II exonuclease-deficient mutant were from > or = 13- to > or = 240-fold higher than for wild-type pol II, depending on the type of error considered. These data suggest that from 90 to > 99% of base substitutions, frameshifts, and large deletions are efficiently proofread by the enzyme. The results of these experiments together with recent in vivo studies suggest an important role for pol II in the fidelity of DNA synthesis in cells.

Base Sequence↗
PubMed1995

Signal-transduction-pathway-specific desensitization of expression of orphan nuclear receptor TIS1.

Induction of many primary-response genes by a variety of stimuli occurs in a transient manner. The precise mechanism responsible for these transient kinetics is not completely understood. We report here that the orphan nuclear receptor, TIS1, which is a potent sequence-specific transcription factor, was transiently induced by the adrenergic agonist isoprenaline in the C2C12 skeletal-muscle cell line. Moreover, we showed that the rapid decline in mRNA level after peak induction was due in part to a specific desensitization of the isoprenaline-mediated induction pathway. Desensitization of the induction response presumably occurred at the level of the receptor, as agents that either bypass the adrenergic receptor or activate alternative signalling pathways were able to induce TIS1 expression in the desensitized cells. However, stimulation by agents that directly activate intracellular enzymes also resulted in the signal-transduction-pathway-specific desensitization of TIS1 inducibility. Our results suggest that the pathway-specific nature of the desensitization process may be important for directing an integrated response to multiple physiological stimuli.

Adrenergic beta-Agonists↗
PubMed1995

Pacemaker current i(f) in adult canine cardiac ventricular myocytes.

1. Single cells enzymatically isolated from canine ventricle and canine Purkinje fibres were studied with the whole-cell patch clamp technique, and the properties of the pacemaker current i(f) compared. 2. Steady-state i(f) activation occurred in canine ventricular myocytes at more negative potentials (-120 to -170 mV) than in canine Purkinje cells (-80 to -130 mV). 3. Reversal potentials were obtained in various extracellular Na+ (140, 79 or 37 mM) and K+ concentrations (25, 9 or 5.4 mM) to determine the ionic selectivity of i(f) in the ventricle. The results suggest that this current was carried by both sodium and potassium ions. 4. The plots of the time constants of i(f) activation against voltage were 'bell shaped' in both canine ventricular and Purkinje myocytes. The curve for the ventricular myocytes was shifted about 30 mV in the negative direction. In both ventricular and Purkinje myocytes, the fully activated I-V relationship exhibited outward rectification in 5.4 mM extracellular K+. 5. Calyculin A (0.5 microM) increased i(f) by shifting its activation to more positive potentials in ventricular myocytes. Protein kinase inhibition by H-7 (200 microM) or H-8 (100 microM) reversed the positive voltage shift of i(f) activation. This effect of calyculin A also occurred when the permeabilized patch was used for whole-cell recording. 6. These results indicate i(f) is present in ventricular myocytes. If shifted to more positive potentials i(f) could play a role in ischaemia-induced ventricular arrhythmias. The negative shift of i(f) in the ventricle might play a role in differentiating non-pacing regions of the heart from those regions that pace.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Prostate-specific antigen is a new favorable prognostic indicator for women with breast cancer.

Prostate-specific antigen (PSA) is thought to be produced exclusively by prostatic epithelial cells and is currently used as a tumor marker of prostatic adenocarcinoma. We recently found that 30% of breast cancers contain PSA immunoreactivity (IR-PSA). To examine the prognostic value of PSA in female breast cancer, we measured IR-PSA in tumor cytosols of 174 breast cancer patients and classified the breast cancers as either PSA positive or PSA negative based on an IR-PSA cutoff level of 0.03 ng/mg. IR-PSA was present in 27% of the patients. IR-PSA presence was associated with early disease stage, small tumors, and estrogen receptor-positive tumors. We used the Cox proportional hazards regression model to analyze survival of patients in association with PSA status and found that patients with IR-PSA-positive tumors had a reduced risk for relapse and death in univariate analysis (P = 0.02 and 0.06, respectively) and a reduced risk for relapse in multivariate analysis (P = 0.03). Further analysis indicated that the effect of IR-PSA on relapse-free survival was evident in node-positive or estrogen receptor-negative patients. Our study suggests that IR-PSA is an independent favorable prognostic marker for breast cancer and may be used to identify a subgroup of estrogen receptor-negative and/or node-positive patients who have good prognoses.

Adult↗
PubMed1995

Expression of the prostate-specific antigen gene by a primary ovarian carcinoma.

We describe a patient with primary ovarian carcinoma that developed after liver transplantation whose tumor was highly positive for prostate-specific antigen (PSA). PSA in tumor tissue was characterized by two immunoassays, HPLC, immunohistochemistry, reverse transcription-PCR, Southern blotting, and DNA sequencing. PSA in the ovarian tumor was present as free, M(r) 33,000 protein (> 90%) and as PSA bound to alpha 1-antichymotrypsin (M(r) 100,000; < 10%). Immunohistochemistry localized PSA in the cytoplasm of epithelial cells of the tumor. Two separate reverse transcription-PCRs for PSA amplified the expected products which hybridized specifically to a PSA cDNA probe on Southern blots. Sequencing of the PCR products, representing the whole coding sequence of the PSA gene, revealed identity with the sequence of PSA cDNA from prostate tissue. These data suggest that the PSA produced by the ovarian tumor was identical in molecular weight and sequence to prostatic PSA. Based on data of tissue culture experiments with breast carcinoma cell lines, we speculate that the PSA gene in the tumor of this patient was up-regulated by the therapeutically administered glucocorticoids after liver transplantation.

Base Sequence↗
PubMed1995

Oral contraceptive-induced expression of prostate-specific antigen in the female breast.

Prostate-specific antigen (PSA) is widely used as a tumor marker of prostatic adenocarcinoma. We recently found that 30% of breast tumors produce PSA and that PSA is a favorable prognostic marker in female breast cancer. We measured immunoreactive PSA in cytosolic extracts of normal breast tissue from eight women receiving no medication and one woman who was receiving no medication and one woman who was receiving the progestin-containing oral contraceptive Brevicon. None of the eight cytosolic extracts of normal breast tissue contained appreciable amounts of immunoreactive PSA. However, left and right breast tissues from the woman receiving Brevicon contained high levels of PSA. This immunoreactive species was shown to have a molecular weight identical to that of seminal PSA. Furthermore, reverse transcription of RNA and polymerase chain reaction amplification produced a 571-base pair cDNA that hybridized to a labeled cDNA PSA probe. Upon sequencing, the cDNA polymerase chain reaction product was found to have 100% homology with cDNA from prostatic tissue. PSA production by breast carcinoma cell lines was achieved after in vitro stimulation with norethindrone and ethinylestradiol. Our data suggest that PSA can no longer be regarded as a specific prostatic protein because it is produced by breast tumors with good prognosis and by normal breast tissue after steroid hormone stimulation.

Base Sequence↗
PubMed1995

Kinectin, an essential anchor for kinesin-driven vesicle motility.

The membrane anchor for the molecular motor kinesin is a critical site involved in intracellular membrane trafficking. Monoclonal antibodies specific for the cytoplasmic surface of chick brain microsomes were used to define proteins involved in microtubule-dependent transport. One of four antibodies tested inhibited plus-end-directed vesicle motility by approximately 90 percent even as a monovalent Fab fragment and reduced kinesin binding to vesicles. This antibody bound to the cytoplasmic domain of kinectin, an integral membrane protein of the endoplasmic reticulum that binds to kinesin. Thus, kinectin acted as a membrane anchor protein for kinesin-driven vesicle motility.

Animals↗
PubMed1995

Mutant p53 protein overexpression is associated with poor outcome in patients with well or moderately differentiated ovarian carcinoma.

BACKGROUND: It has been shown that the p53 gene is mutated in 30-80% of ovarian carcinomas and that the genetic alterations most often manifest as an accumulation of mutant p53 protein in tumor tissue. The prognostic significance of these findings for patients with ovarian cancer, however, must be established clearly. METHODS: Mutant p53 protein in 90 consecutive epithelial ovarian carcinomas was quantitatively analyzed using a time-resolved immunofluorometric procedure. In contrast to immunohistochemical techniques, this method uses two anti-p53 antibodies. The Cox model was used to evaluate the strength of the associations between the prognostic markers and disease relapse or death at univariate and multivariate levels. Kaplan-Meier survival curves were calculated for patients who were p53-positive or negative and for subgroups with a different clinical stage, histologic grade, or residual postsurgical tumor. RESULTS: The positivity rates for p53 included 1/21 (5%) with Stage I disease, 1/6 (17%) with Stage II, 29/51 (57%) with Stage III, and 8/12 (67%) with Stage IV (total = 39/90, 43%). Patients with p53-negative tumors had a significantly longer disease free survival than did patients with p53-positive tumors (P = 0.03); these results were similar for overall survival (P = 0.06). Multivariate analysis revealed that the presence of postsurgical residual tumor was the only predictor significantly associated with poor patient outcome. However, when patients were divided into groups based on histologic grade, patients with well (G1) and moderately (G2) differentiated tumors had a significantly higher risk of cancer relapse and death if mutant p53 protein was present in their tumors compared with patients who were negative for mutant p53 protein (< 0.01). CONCLUSIONS: The immunofluorometric measurement of mutant p53 protein accumulation in epithelial ovarian carcinomas of a low histologic grade was associated significantly with an increased risk for cancer relapse and death. A similar trend also was suggested for early stage disease and in the absence of residual tumor after surgery. These increased risks, however, were not found for patients with high grade or advanced stage cancer or for those with residual tumor. To the authors' knowledge, this is the first report suggesting that p53 tumor protein accumulation is a marker of poor prognosis in a subset of patients with ovarian cancer.

Adult↗
PubMed1995

Nucleotide sequence and peptide motifs of mouse uromodulin (Tamm-Horsfall protein)--the most abundant protein in mammalian urine.

The mouse uromodulin cDNA sequence was sequenced. The predicted peptide sequence is 642 amino acids long and contains several modular components including four epidermal growth factor like repeats, one betaglycan-like domain (ZP domain), and a consensus sequence for attachment of a glycosyl-phosphatidyl-inositol anchor. An arginine-glycine-aspartate tripeptide reported for rat and human sequence is absent in the mouse. There are several potential sites for post-translational modification.

Amino Acid Sequence↗
PubMed1995

Self-assembly of a quinobenzoxazine-Mg2+ complex on DNA: a new paradigm for the structure of a drug-DNA complex and implications for the structure of the quinolone bacterial gyrase-DNA complex.

The quinobenzoxazine compounds A-62176 and A-85226 belong to a novel class of antineoplastic agents that are catalytic inhibitors of topoisomerase II and also structural analogs of the antibacterial DNA gyrase inhibitor Norfloxacin. In vitro studies have shown that their antineoplastic activity is dependent upon the presence of divalent metal ions such as Mg2+ and Mn2+, although the precise role of these ions in the mechanism of action is unknown. In this study we have investigated the structures of the binary complex between the quinobenzoxazines and Mg2+ and the ternary complex between quinobenzoxazine-Mg2+ and DNA. The stoichiometry of the binary and ternary complexes and the biophysical studies suggest that a 2:2 drug:Mg2+ complex forms a "heterodimer complex" with respect to DNA in which one drug molecule is intercalated into DNA and the second drug molecule is externally bound, held to the first molecule by two Mg2+ bridges, which themselves are chelated to phosphates on DNA. There is a cooperativity in binding of the quinobenzoxazines to DNA, and a 4:4 drug:Mg2+ complex is proposed in which the two externally bound molecules from two different 2:2 dimers interact via pi-pi interactions. The externally bound quinobenzoxazine molecules can be replaced by the quinolone antibacterial compound Norfloxacin to form mixed-structure dimers on DNA. Based upon the proposed model for the 2:2 quinobenzoxazine:Mg2+ complex on DNA, a parallel model for the antibacterial quinolone-Mg2(+)-DNA gyrase complex is proposed that relies upon the ATP-fueled unwinding of DNA by gyrase downstream of the cleavable complex site. These models, which have analogies to leucine zippers, represent a new paradigm for the structure of drug-DNA complexes. In addition, these models have important implications for the design of new gyrase and topoisomerase II inhibitors, in that optimization for structure-activity relationships should be carried out on two different quinolone molecules rather than a single molecule.

Animals↗
PubMed1995

Derivatives of cis-2-amino-8-hydroxy-1-methyltetralin: mixed 5-HT1A-receptor agonists and dopamine D2-receptor antagonists.

(1S,2R)-8-Hydroxy-1-methyl-2-(dipropylamino)tetralin [(1S,2R)-3] has been previously characterized as a selective and potent but partial 5-HT1A-receptor agonist. In the present study, we have prepared derivatives of (1S,2R)- and (1R,2S)-3 in which various C8-substituents have been introduced. In addition, the enantiomers of the N-isopropyl-N-n-propylamino derivative of 3 were prepared. The new derivatives were tested in vivo by use of behavioral and biochemical tests in rats. In addition, the affinity of the compounds was studied by competition experiments with [3H]-8-OH-DPAT in rat brain tissue. The only new derivative which behaved like a selective 5-HT1A-receptor agonist was the C8-carboxamide derivative (1S,2R)-13. The other active derivatives, including (1S,2R)-3, have more complicated pharmacological profiles and may be best characterized as mixed 5-HT1A-receptor agonists/dopamine D2-receptor antagonists.

Animals↗
PubMed1995

Immunoreactive prostate-specific antigen in lung tumors.

Prostate-specific antigen (PSA) is a glycoprotein produced by the epithelial cells of the prostate. PSA is currently used clinically to diagnose and monitor prostate carcinoma. In previous work we have demonstrated that 30% of breast tumors and, more rarely other tumors, contain significant amounts of PSA. PSA appears to be a favorable prognostic indicator in breast cancer. Here, using a sensitive assay, we demonstrated for the first time that lung adenocarcinomas and squamous cell carcinomas also contain PSA. PSA in lung tumor extracts was present mainly in its 33 KDa form (free PSA), at levels measurable by commercial methods. The presence of PSA was associated more closely with male patients and adenocarcinomas. The physiological role of PSA in lung tissue and the prognostic significance of PSA in lung cancer remain to be determined. These and our previous data as well as reports by other groups support the view that PSA is a ubiquitous biochemical marker of steroid hormone action.

Adenocarcinoma↗